This invention pertains to a hydroformylation process to prepare a non-aqueous hydroformylation product composition containing one or more aldehyde products and a rhodium-organophosphorus ligand complex, and thereafter a phase separation of the one or more aldehyde products from the non-aqueous hydroformylation reaction product composition with improved separation and recovery of rhodium. The invention is suitably applied to non-aqueous reaction product compositions derived from hydroformylation of olefinically-unsaturated fatty acid esters (FAEs) obtained from seed oils.
Seed oils comprise a mixture of saturated and unsaturated fatty acid esters. The unsaturated fatty acid esters may contain from 1 to 3 olefinic bonds. As is well known, an ester comprises a product of a reaction between a carboxylic acid and an alcohol; therefore, an ester contains a molecular fragment derived from the carboxylic acid and a molecular fragment derived from the alcohol. In seed oils the alkanol is the trihydric alcohol glycerol; however, fatty acid esters of glycerol are difficult to process industrially due to their high molecular weight. Consequently, seed oils are typically transesterified with lower alkanols, which hereinafter refers to an alkanol of from one to about eight carbon atoms (C1-8), such as methanol or ethanol, to obtain the corresponding mixture of saturated and unsaturated fatty acid esters of the lower alkanol, which due to their lower molecular weight are more amenable to chemical processing. As is known in the chemical art, “transesterification” refers to replacement of the alcohol fragment of an ester with a different alcohol fragment. Henceforth, unless otherwise noted, the words “unsaturated fatty acid ester(s)” will refer to unsaturated fatty acid ester(s) of a lower alkanol (transesterified seed oils), not the glycerol esters or the seed oils themselves.
The art describes the hydroformylation of a reactant olefin consisting of a mono-unsaturated fatty acid ester with carbon monoxide and hydrogen (e.g., synthesis gas) in the presence of a rhodium-organophosphorus ligand complex catalyst and free organophosphorus ligand to produce an aldehyde product having one additional carbon atom in the fatty acid chain (“monoformyl product”) as compared with the reactant olefin. When the reactant olefin is a di-unsaturated or tri-unsaturated fatty acid ester, hydroformylation may occur at each olefinic unsaturation to yield dialdehydes (“diformyl product”) and trialdehydes (“triformyl product”). The hydroformylation of a mixture of unsaturated fatty acid esters derived from seed oils produces a mixture of monoformyl, diformyl, and triformyl (aldehyde) products. Generally, not every olefinically-unsaturated bond is converted to aldehyde; thus the product derived from the aforementioned mixtures typically contains, in addition to one or more aldehyde products, a quantity of unconverted mono-unsaturated and poly-unsaturated (di- and/or tri-unsaturated) fatty acid esters. As an unavoidable side reaction, a portion of the unconverted poly-unsaturated fatty acid esters, which initially exist typically in unconjugated form, is isomerized to the corresponding conjugated isomers. One skilled in the art recognizes that an unconjugated olefin is one in which two C═C double bonds are separated by more than one C—C single bond; whereas a conjugated olefin is one in which two C═C double bonds are separated by only one C—C single bond.
The aforementioned mixtures of monoformyl, diformyl, and triformyl products derived from the hydroformylation of mixtures of unsaturated fatty acid esters can be reacted via hydrogenation or hydroamination processes to yield the corresponding alcohol, amine, or aminoalcohol derivatives, which can be condensed to form oligomeric polyols, polyamines, or polyaminoalcohols. The latter poly-functional compounds find utility in the manufacture of industrially useful polymers, most notably, polyurethanes. With regard to the aforementioned hydroformylation chemistry and subsequent derivatives, reference is made to International Patent Application Publications WO 2004-A1-096744 and WO 2004-A1-096882.
As illustrated by the above chemistry, seed oils can provide sustainable, alternative feedstocks to more conventional petroleum-based feedstocks for use in manufacturing industrially useful chemicals. Nevertheless, commercialization of chemical processes starting from the hydroformylation of fatty acid esters derived from seed oils will depend upon an efficient method of separating the resulting aldehyde product(s) from the hydroformylation reaction product composition. Moreover, commercialization also depends upon an efficient separation and recovery of rhodium. Even a small loss of rhodium into the aldehyde product would necessitate supplying make-up rhodium to the hydroformylation process; else the rhodium catalyst would be continuously depleted. Since rhodium is one of the most expensive metals, loss of rhodium is not acceptable. Furthermore, rhodium residue in the aldehyde product can lead to downstream problems; for example, rhodium is known to interfere with hydrogenation of the aldehyde product.
One skilled in the art may recognize that the hydroformylation of fatty acid esters is more readily conducted in a non-aqueous reaction medium, because fatty acid esters possess little, if any, solubility in water. Hydroformylations wherein the olefinically-unsaturated reactant and a rhodium-organophosphorus ligand complex catalyst are solubilized in a non-aqueous medium (i.e., organic solvent) are well known. Early references to non-aqueous processes disclosed rhodium-organophosphorus ligand complex catalysts wherein the organophosphorus ligand consisted of a neutral organophosphine or organophosphite, that is, an organophosphine or organophosphite free of an ionic charge, such as, triphenylphosphine. While such processes have been effective in hydroformylating lower olefins, namely olefins having from two to about 5 carbon atoms (C2-5), their application is curtailed when hydroformylating high molecular weight olefins due to difficulties in separating high molecular weight aldehyde products from the hydroformylation reaction product composition. Distillation cannot be used for the separation, for at least one reason that the rhodium-organophosphorus ligand complex tends to degrade at the high temperatures needed for the distillation. Moreover, the problem is exacerbated when the product to be separated from the hydroformylation reaction product composition comprises aldehyde products derived from fatty acid esters, because the resulting aldehydes possess molecular weights entirely too large for separation by distillation methods.
With reference to the above and for the purposes of this invention, the terms “high molecular weight olefin” and “high molecular weight olefinically-unsaturated fatty acid ester” are defined as an olefinic compound, or fatty acid ester as the case may be, having 7 or more carbon atoms. Likewise, the term “high molecular weight aldehyde product” is defined as an aldehyde product having 8 or more carbon atoms.
U.S. Pat. No. 5,180,854 discloses a process for phase separating and recovering a high molecular weight aldehyde product from a non-aqueous hydroformylation reaction product composition comprising the aldehyde product and a rhodium-organophosphorus ligand complex, free organophosphorus ligand, and an organic solubilizing agent for the complex and the free ligand. In the disclosed process, the organophosphorus ligand consists of an ionically-charged organophosphine, the term “ionically-charged” being described in detail hereinafter. The disclosed method involves adding water, and optionally a nonpolar solvent, to the non-aqueous hydroformylation reaction product composition and by phase separation obtaining a nonpolar phase consisting essentially of the aldehyde product and optional nonpolar solvent and a polar phase consisting essentially of the added water, the rhodium-organophosphorus ligand complex, the free organophosphorus ligand, and the organic solubilizing agent. The ionically-charged organophosphine ligand possesses an advantageous solubility in water; thus rhodium and ligand are separated from the high molecular weight aldehyde product. Being insoluble in water, the aldehyde product remains in the nonpolar phase.
While the method of U.S. Pat. No. 5,180,854 has been adopted for use with reaction product compositions derived from hydroformylating high molecular weight mono-olefins, we have now found that the method remains inadequate when applied to reaction product compositions derived from the hydroformylation of mixtures of high molecular weight mono-olefins and polyolefins, as are found in mixtures of unsaturated fatty acid esters derived from seed oils. We have further recognized that when the reaction product composition contains one or more aldehyde products and one or more conjugated polyolefins, then after phase separation, the quantity of rhodium metal in the nonpolar phase containing the aldehyde products is unacceptably high. The words “unacceptably high” mean that the concentration of rhodium in the nonpolar phase is greater than about 3.0 parts per million (ppm) by weight, based on the weight of the nonpolar phase.
We have further found that rhodium can be recovered with an acceptable efficiency from a hydroformylation reaction product composition containing high molecular weight conjugated polyolefins, if the reaction product composition is produced in a hydroformylation process operating at synthesis gas pressures of 600 psia (4,137 kPa) or higher. Operating the hydroformylation at a high pressure is not desirable, however, because higher pressure is associated with higher operating costs, more expensive equipment, and waste of resources.
In view of the above, it would be desirable to discover a non-aqueous hydroformylation process, preferably in continuous operation, combined with an improved separation stage for separating one or more aldehyde products from a non-aqueous hydroformylation reaction product composition comprising the one or more aldehyde products and a rhodium-organophosphorus ligand complex. It would be more desirable if the hydroformylation process employed low operating pressures, for example, pressures ranging from about 250 psia (1,724 kPa) to about 450 psia (3,103 kPa), so as to avoid the costs of higher pressurized processes. It would be even more desirable if the separation stage were to separate and recover rhodium from the hydroformylation reaction product composition with a high degree of efficiency. For the purposes of this invention, the words “high degree of efficiency” mean that after implementing the separation an aldehyde-containing nonpolar phase is recovered containing less than about 1.0 ppm rhodium, by weight, based on the weight of the nonpolar phase. Finally, it would be most desirable if the method could provide a high efficiency of rhodium separation and recovery when using mixtures of high molecular weight aldehydes containing conjugated polyolefins as found, for example, in reaction product compositions derived from the hydroformylation of unsaturated fatty acid esters obtained from seed oils.
If the aforementioned effects could be achieved, rhodium would be concentrated essentially in an aqueous phase from which the rhodium could be recovered for direct catalyst recycle to the hydroformylation process. Such a separation method would also provide for a purer aldehyde product, would minimize the disadvantageous effects of residual rhodium on downstream aldehyde processing, and would minimize the amount of make-up rhodium supplied to the hydroformylation process. Moreover, a low pressure hydroformylation process would minimize engineering costs and waste of resources. As a consequence, commercialization of industrially useful processes starting from the hydroformylation of unsaturated fatty acid esters derived from seed oils may move closer to realization.